UNIVERSITY    OF    CALIFORNIA     AGRICULTURAL   EXPERIMENT  STATION 

~~.    .    ~~-     .«..-     .  «*_._..  ..  .....  BENJ.    IDE    WHEELER,    PRESIDENT 

COLLEGE   OF  AGRICULTURE 

THOMAS    FORSYTH    HUNT,   Dean  and  Director 

BERKELEY  h.  e.  van  norman,  vice-director  and  dean 

University  Farm  School 


CIRCULAR  No.  200 
May,  1918 


GROWING  THE  FALL  OR  SECOND  CROP 
OF  POTATOES  IN  CALIFORNIA 

By  STANLEY  S.  EOGERS 


It  is  possible  and  profitable,  over  a  large  portion  of  California,  to 
grow  a  second  or  fall  crop  of  potatoes,  and  this  practice  should  be 
encouraged  where  conditions  are  favorable,  for  practical  experience 
has  shown  that  a  heavier  yield  of  better  quality  is  realized  than  in 
the  case  of  early  spring  potatoes. 

It  is  difficult  to  store  potatoes  successfully  during  the  warmer 
months,  but  those  maturing  in  the  fall  may  be  kept  in  a  satisfactory 
condition  until  the  following  spring,  which  is  often  an  advantage  to 
the  grower.  As  a  rule,  higher  prices  prevail  during  the  winter  and 
spring  than  are  offered  in  the  summer;  this  coupled  with  the  larger 
yields  obtained,  appears  to  be  very  encouraging  for  the  future  pro- 
duction of  fall  potatoes. 

It  is  imperative,  however,  that  the  soil  be  adapted  to  the  needs 
of  this  crop,  and  that  sufficient  irrigation  facilities  be  available  so 
that  the  water  may  be  applied  when  needed.  The  absence  of  heavy 
frosts  up  to  the  middle  of  November  is  also  an  important  condition. 

Hoiv  to  Obtain  Seed. — The  seed  may  be  obtained  from  the  potatoes 
stored  over  winter,  or  from  the  spring  crop  of  the  same  year.  Under 
ordinary  conditions  the  latter  source  of  seed  is  preferable. 

Growing  Seed  for  Second  Crop. — When  home-grown  seed  is  used, 
the  crop  should  be  planted  as  soon  in  the  spring  as  possible,  the  exact 
time  depending  largely  upon  the  climatic  conditions.  Under  central 
California  conditions  the  seeding  may  be  done  during  February  and 
March,  but  in  the  warmer  sections  it  is  possible  to  advance  the  time 
of  planting  considerably.  In  the  vicinity  of  Sacramento,  the  planting 
is  done  from  February  1  to  March  15. 

If  an  early  maturing  variety,  such  as  the  American  Wonder,  is 
used,  the  crop  may  be  dug  during  the  latter  part  of  June  to  the  first 
week  in  July.  When  using  this  crop  for  seed,  experience  has  shown 
that  it  should  be  harvested  before  full  maturity.  The  most  desirable 
time  to  harvest  is  when  the  vines  are  changing  from  a  yellow  to  a 
brownish  color. 


Harvesting  and  Curing  the  Seed. — If  the  crop  is  harvested  at  the 
period  shown  above,  the  potatoes  will  not  be  fully  matured  and  the 
skin  will  slip  very  easily.  After  digging  they  should  be  exposed  to 
the  sun  from  one-half  to  one  hour  before  being  picked  up.  If  the  day 
is  very  hot,  care  should  be  taken  not  to  allow  them  to  be  on  the  ground 
too  long,  as  they  will  sunburn  very  easily  and  become  unfit  for  food, 
storage,  or  seed. 

After  the  crop  has  been  exposed  to  the  sun  the  desirable  length  of 
time,  the  seed  should  be  placed  immediately  in  piles  from  two  to  four 
feet  high  and  covered  with  straw  to  a  depth  of  from  six  inches  to  one 
foot.  These  heaps,  or  stacks,  should  be  sprinkled  each  day  or  so, 
putting  on  enough  water  to  soak  into  them  thoroughly,  but  being 
careful  that  no  excess  moisture  is  allowed  to  accumulate,  for  fear  of 
rotting  the  potatoes.     The  water  may  be  applied  through  the  straw. 

If  there  is  no  danger  of  tuber-moth  infestation,  these  piles  may 
be  made  under  a  tree  or  shade  where  they  will  be  protected  from 
the  heat,  or  at  least  partially  shaded.  Where  this  pest  is  troublesome, 
it  is  best  to  store  the  potatoes  in  a  building  where  the  moth  can  not 
gain  entrance,  or  cover  the  piles  each  night  with  canvas. 

The  length  of  time  the  potatoes  should  remain  in  these  piles  is 
somewhat  dependent  upon  the  condition  of  the  tubers,  climate  and 
season,  but  generally  from  one  to  two  weeks  is  sufficient.  After  being 
removed  they  should  be  dipped,  cut  and  planted  as  soon  as  possible, 
for  the  longer  they  are  exposed,  the  weaker  will  be  their  germination 
power. 

The  selection  of  seed  potatoes  should  be  made  at  the  time  of  har- 
vesting, and  it  is  best  to  dig  a  certain  portion  of  the  crop  by  hand, 
keeping  the  individual  hills  separated,  and  to  select  from  these  the 
potatoes  best  suited  for  future  propagation.  If  this  method  is  pur- 
sued, the  condition  of  the  hill,  as  a  whole,  should  be  noted  and  not 
the  individual  potato.  If  the  grower  does  not  wish  to  use  the  hill 
selection,  he  should  at  least  save  only  those  potatoes  which  conform 
closely  to  the  ideal  of  the  type  and  variety;  a  medium  sized  potato, 
free  from  disease,  will  be  found  more  advantageous  than  the  very 
small  or  large  tubers. 

The  proper  selection  of  the  seed  is  of  extreme  importance;  where 
this  is  carried  on  carefully  and  thoroughly,  it  will  pay  the  grower  to 
select  his  own  seed  from  one  season  to  another.  At  the  University 
Farm  vegetable  garden,  home-grown,  selected  potatoes  have  been  used 
for  four  years  and  the  quality  of  the  eight  crops  produced  has  im- 
proved regularly.  Should  home-grown  seed  be  used  continually, 
without  proper  regard  to  selection,  it  is  probable  that  the  quality 
would  soon  deteriorate  to  a  degree  where  new  seed  would  have  to  be 
imported. 

Preparation  of  the  Soil. — It  is  sometimes  difficult  to  obtain  a  satis- 
factory stand  of  potatoes  when  planting  during  very  hot  weather. 
This  is  due  to  poor  curing  of  the  seed  and  especially  to  an  unfavorable 
condition  of  the  soil.  In  preparing  the  field  for  planting  the  great 
problem  is  to  cool  the  soil  sufficiently  so  that  the  seed  will  not  be 
burned.     Following  is  the  method  commonly  used  by  many  of  the 


market  gardeners  and  at  the  University  Farm,  and  appears  to  be 
entirely  satisfactory  for  the  interior  valleys  and  warmer  sections  of 
the  state. 

From  one  week  to  ten  days  before  planting,  the  exact  time  depend- 
ing largely  upon  the  character  of  the  soil,  the  field  should  be  irrigated 
very  heavily,  so  that  the  soil  is  thoroughly  saturated.  A  second  irri- 
gation is  given  from  two  to  four  days  before  planting  and  as  the 
chief  advantage  of  this  irrigation  is  to  cool  the  soil,  a  small  amouut 
of  water  is  used.  Where  possible,  the  land  should  be  flooded  rather 
than  applying  the  water  in  furrows.  It  is  not  customary  to  work  the 
land  between  irrigations. 

Planting. — Just  previous  to  planting,  the  potatoes  should  be  im- 
mersed from  one  and  one-half  to  two  hours  in  a  corrosive-sublimate 
solution  of  a  strength  of  one  ounce  of  the  material  to  eight  gallons  of 
water.  Extreme  care  should  be  exercised  in  handling  this  dip,  as  it 
is  very  poisonous.  A  wooden  receptacle,  such  as  a  barrel,  should  be 
used  for  this  purpose. 

As  soon  as  the  soil  is  in  proper  condition,  the  field  is  plowed  to  a 
depth  of  eight  to  twelve  inches  and  the  potatoes  immediately  planted. 
In  planting  large  areas,  better  success  will  be  attained  if  the  field  is 
worked  in  small  tracts,  planting  as  soon  as  possible  after  plowing. 
The  seed  should  be  put  in  the  ground  at  least  five  inches  deep,  prefer- 
ably six  or  seven  inches,  in  order  to  protect  it  as  much  as  possible 
from  the  heat  and  to  prevent  drying.  Heavier  seeding  should  be 
practiced  in  planting  at  this  season  than  is  customary  when  seeding 
under  more  congenial  growing  conditions.  At  least  eight  sacks  of 
medium  sized  potatoes  per  acre  should  be  used. 

The  time  of  planting  is  governed  by  the  locality  and  time  at  which 
the  first  crop  is  in  condition  to  be  dug.  For  the  central  interior 
valleys  the  planting  season  extends  from  July  7  to  August  1.  In  the 
southern  part  of  the  state  the  planting  may  be  done  from  July  1  to 
August  10.  Many  potatoes  are  planted  after  the  dates  given  above, 
but  this  is  done  at  a  considerable  risk,  owing  to  the  liability  of  early 
frosts  which  may  kill  the  plants  before  they  are  mature,  resulting  in 
a  partial  or  total  loss  of  the  crop. 

In  many  of  the  hot  interior  valleys,  the  potatoes  maturing  in 
June  and  July  are  often  internally  discolored.  This  condition  is 
known  as  the  Internal  Brown  Streak,  and  is  not  transmitted  through 
the  seed,  so  that  the  affected  tubers  may  be  used  for  this  purpose. 
The  grower,  however,  should  not  confuse  this  condition  with  several 
of  the  parasitic  diseases  which  discolor  the  potato,  making  it  absolutely 
unfit  for  seed.  Should  any  doubt  exist,  a  sample  may  be  submitted 
to  the  University  of  California,  College  of  Agriculture. 

Future  Care  of  Crop. — The  future  care  differs  only  slightly  from 
the  methods  used  for  growing  the  spring  crop.  After  planting,  the 
field  should  be  harrowed  at  least  once  a  week  until  the  plants  appear, 
for  every  effort  must  be  made  to  keep  as  much  moisture  as  possible  in 
the  soil,  since  it  is  unwise  to  irrigate  before  a  month  to  six  weeks 
after  planting  and  the  loss  of  moisture  during  the  heat  of  the  summer 
is  very  rapid.     As  soon  as  the  plants  are  four  to  eight  inches  high, 


the  field  should  be  irrigated  and  a  second  irrigation  is  given  about 
the  time  the  plants  are  in  full  bloom.  It  is  often  desirable  to  apply 
the  water  a  third  time,  viz.,  before  the  vines  start  to  mature. 

Harvesting. — When  an  early  or  medium-early  variety  is  used,  the 
crop  may  be  harvested  in  November.  Should  it  be  desirable  to  store 
the  potatoes,  they  should  not  be  dug  until  the  vines  have  been  killed 
by  frost,  for  in  order  that  the  crop  may  be  held  successfully,  it  should 
be  thoroughly  matured.  Should  rain  come  before  the  crop  is  har- 
vested, the  tubers  will  not  be  injured,  provided  the  soil  drainage  is 
such  that  the  water  will  not  stand  on  the  field.  During  periods  in 
which  frosts  are  likely  to  appear,  the  potatoes  should  not  be  left 
exposed  over  night.  It  is  best  to  leave  them  on  the  ground  from  two 
to  four  hours  before  sacking,  in  order  that  they  may  dry;  this  will 
also  help  to  mature  them  properly. 

Storing. — There  are  several  methods  for  storing  during  the  winter. 
Some  leave  the  crop  in  piles  in  the  field,  protected  from  frost  by  straw 
or  sacks.  This  method  is  only  used  where  the  soil  is  of  a  sandy  nature 
so  that  no  excess  water  will  accumulate.  The  most  common  practice 
for  keeping  potatoes  in  California  over  winter  is  to  put  them  in  sacks 
and  store  in  a  weather-proof  building.  This  should  be  well  ventilated, 
rain-proof,  and  as  dark  as  possible.  During  warm  days  the  house 
should  be  closed  and  opened  during  the  nights,  provided  the  tempera- 
ture is  not  too  severe. 

The  third  method  is  storing  the  potatoes  in  crates,  placed  in  a 
suitable  building.  Even  under  good  storage  conditions,  losses  are 
sometimes  sustained ;  in  order  to  store  potatoes  in  a  satisfactory  man- 
ner, they  must  be  fully  matured  when  dug  and  kept  out  of  the  light 
as  much  as  possible. 

Varieties. — The  American  Wonder  and  White  Rose  varieties  are 
most  commonly  used  when  two  crops  are  grown  in  one  season.  The 
former  is  produced  throughout  the  Sacramento  and  San  Joaquin 
valleys,  and  southern  California.  The  latter  is  used  chiefly  in  the 
southern  part  of  the  state. 

SUMMARY 

The  production  of  a  second  or  fall  crop  of  potatoes  in  many  sec- 
tions of  California  should  be  encouraged. 

Potatoes  ripening  in  the  fall  will  keep  much  longer  than,  those 
maturing  during  the  spring  or  summer. 

It  is  preferable  to  use  the  potatoes  maturing  in  the  spring  for  seed 
from  which  to  grow  the  fall  crop. 

A  second  crop  of  potatoes  should  be  grown  only  where  the  soil 
is  adapted  to  its  needs  and  where  adequate  irrigation  is  available. 

It  is  often  difficult  to  procure  a  satisfactory  stand  of  plants  when 
planting  during  the  extreme  heat.  This  may  be  largely  overcome  by 
curing  the  seed  properly,  and  irrigating  twice  just  previous  to 
planting. 

In  central  California,  the  seed  should  be  planted  between  July  7 
and  August  1 ;  in  southern  California  from  July  1  to  August  10. 

Under  ordinary  conditions  the  crop  will  be  ready  to  harvest  during 
November,  but  should  not  be  dug  until  the  plants  have  fully  matured. 


